To identify patterns of service provision in the United States, electrodiagnostic encounters were characterized by analyzing data from the 1998 MarketScan Commercial Claims & Encounters Database (The MEDSTAT Group). Electrodiagnostic-related claims were identified using CPT codes for nerve conduction studies, electromyography, and somatosensory evoked potentials. Over 130,000 electrodiagnostic claims representing 48,207 separate electrodiagnostic encounters were identified. Neurologists accounted for the highest percentage of physician providers (23.6%), followed closely by physiatrists (22%). Physiatrists performed the services at a higher rate than any other provider (886.3 studies per 100 practicing physiatrists). Electrodiagnostic encounters by nonphysician providers accounted for 16.9% of all studies. Physical therapists were the dominant nonphysician providers of electrodiagnostic services (9.3%), followed by podiatrists (5.5%). Physician providers had a median of three claims per encounter compared with one claim per encounter for nonphysician providers. The relatively large proportion of studies conducted by nonphysicians, as well as their limited extent of testing, raises concerns about the quality of care for these patients. These quality issues should be addressed in future studies.